Zeolites are crystalline aluminosilicate molecular sieves which have a microporous three-dimensional framework structure. In general, the crystalline zeolites are formed from corner-sharing AlO.sub.2 and SiO.sub.2 tetrahedra and are characterized by having pore openings of uniform dimensions, having a significant ion-exchange capacity and being capable of reversibly desorbing an adsorbed phase which is dispersed throughout the internal voids of the crystal without significantly displacing any atoms which make up the permanent crystal structure.
Zeolites can be represented on an anhydrous basis, by the empirical formula EQU M.sub.2/n O:Al.sub.2 O.sub.3 :XSiO.sub.2
where M is a cation having the valence n, X is generally equal to or greater than 2. In naturally occurring zeolites, M can be Li, Na, Ca, K, Mg and Ba. The M cations are loosely bound to the structure and frequently can be completely or partially replaced with other cations by conventional ion exchange techniques. Currently over 150 species of both naturally occurring and synthetic zeolites are known.
Other crystalline microporous compositions are known which are not zeolitic, i.e., do not contain AlO.sub.2 tetrahedra as essential framework constituents, but which exhibit the ion-exchange and/or adsorption characteristics of the zeolites. These include 1) a pure silica polymorph, silicalite, having a neutral framework containing neither cations nor cation sites as disclosed in the U.S. Pat. No. 4,061,724; 2) crystalline aluminophosphate compositions disclosed in U.S. Pat. No. 4,310,440; 3) silicon substituted aluminophosphates as disclosed in U.S. Pat. No. 4,440,871; 4) metal substituted aluminophosphates as disclosed in U.S. Pat. No. 4,853,197; and 5) metal sulfide molecular sieves disclosed in U.S. Pat. No. 4,880,761.
U.S. Pat. No. 4,440,871 discloses a class of silicoalumino phosphates which are identified by the acronym SAPO and which have different structures as identified by their x-ray diffraction pattern. The structures are identified by a numerical number after SAPO. Thus, the '871 reference discloses the preparation of SAPO-5, SAPO-11, SAPO-16, SAPO-17, SAPO-20, SAPO-34, SAPO-35, SAPO-37, SAPO-40, SAPO-42, SAPO-44, SAPO-31, and SAPO-41. Applicant has synthesized two new species in the SAPO family, namely SAPO-36 and SAPO-56. Although the 36 structure has been synthesized in the MeAPO and the MeAPSO families, where Me is magnesium, zinc, manganese or cobalt, there are no known reports of the 36 structure being synthesized in the SAPO family. Applicant is thus the first to synthesize the 36 and 56 structures in the SAPO family. Both of these structures are observed to have unique adsorptive and catalytic properties as will be discussed in more detail herein.